The present invention relates to a current cutoff circuit and an electric steering wheel lock that prevents a load from overheating.
Steering wheel locks are installed in automobiles to prevent automobile theft in the prior art. A typical steering wheel lock is an electric steering wheel lock 51 such as that shown in FIG. 1. The steering wheel lock 51 includes a central processing unit (CPU) 52, a relay 53 controlled by the CPU 52, a motor 55 connected to the relay 53, and a lock bar 54 that engages a steering shaft (not shown) and that is moved by the motor 55. The relay 53 includes a switch 56 connected to the positive terminal of the motor 55 and a switch 57 connected to the negative terminal of the motor 55. The switches 56 and 57 each have a contact switched between a battery terminal 58a and a ground terminal 58b. 
As shown in the state of FIG. 1, current does not flow to the motor 55 and the lock bar 54 does not move when the contacts of the two switches 56 and 57 are connected to the ground terminal 58b. To set the steering wheel lock 51 in a locked state, that is, to lock the steering wheel shaft, the CPU 52 switches the contact of the switch 56 to the battery terminal 58a. This produces forward rotation with the motor 55 and engages the lock bar 54 with a groove formed in the steering shaft. In this manner, the steering wheel lock 51 is set in the locked state. To set the steering wheel lock 51 in an unlocked state from the inactivation state of FIG. 1, the CPU 52 switches the contact of the switch 57 to the battery terminal 58a. This produces reverse rotation with the motor 55 and disengages the lock bar 54 from the groove formed in the steering shaft. In this manner, the steering wheel lock 51 is set in the unlocked state.
However, in such type of relay 53, unanticipated excessive current may flow though the motor circuit. In addition, there is a possibility of the contacts of the switches 56 and 57 fusing due to deficient soldering in the switches 56 and 57. For example, the contact of the switch 56 may be fused on the battery terminal 58a. In such a state, the contact of the switch 56 cannot be switched to the ground terminal 58b. Thus, current to the motor 55 cannot be cut off. In this case, current continuously flows to the motor 55 and overheats the motor 55.